postmortems & mysteries

Last thoughts on a lost colony

So many responses! And theories galore—everything from tracheal mites to alien abduction. I promised to give my own opinion on the cause of death, but please remember that there is a lot of experience reflected in the posted answers. My own opinion is just that, so you should not discount what others have to say.

Several of you wished you had more information about the history of the colony, its size, mite treatments, last queen sighting, etc. I agree those things would be helpful, but knowing nothing is a common starting place. Detectives in a real crime scene usually begin with no history, and hive detectives often have the same handicap.

The final cause of death

My own conclusion is that the final cause of death—the thing that took out the last tiny cluster—was cold. As you know, a cluster of bees stays warm by vibrating their wing muscles to create heat, and the warm bees on the inside rotate positions with the cold bees on the outside. Aaron’s tiny cluster is too small to have an inside and an outside, so all the bees are going to be cold.

Once the bees become chilled, they can’t move, which renders it impossible to retrieve food even if it is close. So you could argue starvation, but in this case I’d say the two conditions were related: the bee cluster was too small to stay warm or to get stored food.

The real cause of death

Nevertheless, the real cause of death occurred much earlier. The few bees shown in the photos were just the hangers on; they were doomed to die and it was just a matter of time.

Trying to figure out why the colony collapsed in the first place is much more difficult. My thought was that the queen died in fall. I say this because there was a fair amount of honey left in the hive. The colony had to be robust enough to defend itself from robbers and yellowjackets right up until the end of flight season.

If the queen had died (or stopped laying) earlier, the colony may have weakened before cold weather arrived, giving predators a chance to rob the hive. If nothing else, Aaron’s other hive would have cleaned it out. But based on the photos, I didn’t see any ragged comb which would indicate robbers or yellowjackets.

The colony had been fairly vigorous at one point because the brood area was large in some of the frames (based on darkened comb) and because there was a fair bit of honey collected in a year when honey collection was not generally good here in western Washington.

Too late for queen replacement

I concluded from this that it was a fairly normal colony that was doing fine until it went queenless in the fall. I assume the queen failed too late in the year for the colony to raise a replacement or, even if they did, it was too late to get her mated.

This leads to the next question: why did the queen die (or stop laying)? Of course, I don’t know. But a lot of queens die in the fall. In my opinion, queens with short lifespans are the result of genetic weakness due to inbreeding. Over and over, I find that queens raised locally outperform and outlive queens shipped from large-scale queen farms. I believe local queens are better adapted and have a more robust gene pool.

But I don’t know the origin of Aaron’s queens, so that is just a blind guess based on seeing lots of production queens die in the fall for no apparent reason.

The Varroa connection

Now, obviously, the bees could have died for other reasons. Based on Aaron’s testimony that he saw no K-wing or deformed wings, at first I thought Varroa was not the primary cause of death. On the other hand, this looks like a classic case of death by Varroa.

Varroa-infected colonies frequently die in the fall as the ratio of mites to bees increases. Also, colonies that collapse from Varroa frequently contain only a few dead bees but lots of honey. The bees that are not infected continue to remove the dead and defend the hive while the colony population dwindles. Although I didn’t see any guanine deposits in the photos, it’s possible they didn’t show up due to the camera angle.

Tracheal mites

I eliminated tracheal mites mostly because they aren’t very common at the moment. In fact, last fall my professor in a beekeeping class did an informal survey of beekeepers from all over North America and found that tracheal mites are rare—even the testing labs are seeing few cases. Many people think that all the miticides used against Varroa may have weakened the tracheal mite population to the point where they aren’t much of a problem.

However, they still occur in certain areas and there is nothing to say that newer, better, stronger tracheal mites will not show up once they develop resistance to all the commonly used miticides. This would not surprise me one bit. If you (Aaron) are worried about your other hive, you can send a sample to a lab for analysis, or I can do it for you.

Mold grows as the bees die

I have to agree with Aaron that I don’t see the mold as cause for concern. Mold is a result of colony death, not a cause of it. Also, there wasn’t much. If ventilation had been a problem, I wouldn’t be surprised to see mold covering every frame. But here, isolated spots of mold are growing on damp pollen and on dead bees. This occurred because once the colony died, the circulation caused by the bees’ wings stopped, and heat generated by the bees’ bodies disappeared. With no heat and no air movement, mold is inevitable.

No “for sure” answer

For what it’s worth, my conclusion is the colony died from a combination of a failed queen and a Varroa mite infestation. It’s very possible that the mite load caused the queen to die, although she could have been offed by poor genetics, injury, or disease. It’s also possible the colony would have died from the mites even if the queen were healthy.

The colony might have been saved by timely Varroa treatments of some type, and a fall brood nest inspection to make sure the queen was present and laying. With today’s queen problems, the fall inspection is imperative.

Again, I want to thank Aaron for allowing me to use his analysis and photos—what a gift! Some of us are reluctant to have our misfortunes pasted all over the internet so, Aaron, you are much appreciated.


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  • Rusty,

    Thank you all so much for sharing your thoughts. As a new beekeeper I have a lot to learn and keep an eye out for.

    I do have a question. I live in Colorado and back in December I ended up with maybe 100-200 bees from a tree that had been cut down. I was harvesting the comb and to my surprise found some bees. There was no honey, pollen or signs of queen. I put them in a box with some of their comb (empty) and fed them. Some of them seem to have pulled through the last cold snap.

    I am considering trying to incorporate them into one of my existing hives but don’t want to stress them out either, just for the sake of a very small number of bees. We have a forecast of a warm week next week so was thinking if I am gonna do it that would be the time. Would you ever consider trying to do this in the middle of winter? Should I just let nature take its course and allow them to die off from cold? I have the two boxes very close to each other so that if I do the merge they should be fine in finding “home”.

    I was thinking of the newspaper between boxes method. I was gonna spray it with sugar water to make it even easier and faster.

    Any feedback is welcome.


    • Greg,

      Sure, I would combine them and, yes, I have combined in mid-winter before. Use newspaper, but be careful of the sugar water. If it’s cold you don’t want to get the bees chilled. Put a small slit in the newspaper, and they will combine in no time.

  • This was my colony exactly last Feb. Still aches, but good to know what happened. I did everything different this year with the new girls (added vents, quilt box) and will put honey reserve on….soon?? Thanks for the postmortem.

  • Hello,

    I acquired a single colony last summer (I know, only one and very late) to see how it would go. And I think my colony lost the queen in the late fall, early winter. I wasn’t aware this could be such a common event and that is why I followed this postmortem with interest.

    The colony is in Portugal, in an area of transition between Mediterranean and temperate climate. Falls can be very mild and true winter is short lived. There is normally a good provision of flowers in early fall, typical of Mediterranean ecosystems where late summer rains lead to a second yearly peak of flowering.

    I had last inspected the hive in the end of October. All seemed well, with plenty of activity in warmer, dry days, so I let it be. Nevertheless I was worried about reserves so was waiting for a sunny day after a very cold spell in December to open the top and have a quick look to the stored honey reserves (I fed substantially all summer to give the colony a chance of building up honey reserves for winter and I think it worked).

    Early in January, I went to have a look at the colony from the outside and was surprised to see a number of drones flying around the entrance. I had been pretty sure that the bees had expelled the previous drone population somewhere in November, when I watched workers preventing drones from returning to the hive, so I wasn’t expecting drones. My first thought was that the queen had died and workers were laying. The day was warm enough so I did a full inspection.

    I didn’t find the queen, but to be honest I never found her in my previous inspections. I found a lot of capped brood, which surprised me, but no eggs and virtually no larvae, just a few. I found small pockets of capped drone brood. But mostly it was workers brood. I then found a fully developed emergency replacement cell, covered with workers, right in the middle of a frame. So my conclusion has been that the queen died. I was in doubt if it could be a case of simply a weak queen that is still present and if there will be a swarm in early February. But after reading about the fall demise of queens I am more inclined for the dead queen hypothesis.

    Reserves were low but still present. A few eucalyptus trees have been flowering profusely around here, enough I think to keep the bees going on warm sunny days. Still, weather took a turn to the worse the last days, with a lot of rain, so I have decided to feed, just to play safe.

    As for the queen replacement, I will have to go with luck. If I had 2 colonies I could try and merge them. But, mistake number one, I only got the one. So, I’m waiting to see what happens.

    I confess I am now a bit afraid to open the hive. Afraid the new queen hasn’t been mated. There were some nice sunny days after I opened the hive but I don’t know if queens wait a few days before going for it. Also inbreeding is a concern as the only drones around are probably the ones the colony produced.

    So, after a very long message, just another example I guess of a queen failing in the fall, something I wasn’t aware could be so prevalent, and I thank you for yet another insight from your excellent blog. I was surprised to see so much capped brood, really a lot, I guess the queen just went for it with a vengeance and that took its final toll.

    Lets see if the colony is able to survive by itself. If there is anything you think i should be doing, your feedback would be appreciated (but I understand the difficulty in answering all the distressed beekeepers that probably appeal to your experience). Thank you for your blog, I keep learning a lot from it even if I didn’t follow the number one advice for new beekeepers: get more than one colony!

    All the best. Pedro

    • Pedro,

      I’d say you’ve done the best you can. If you have drones flying, there will be other drones out there. Bee colonies live where you least expect it and both queens and drones will fly long distances to mate. Your colony could still pull through. Let me know what happens.

      • Thanks for your reply. Yesterday I saw a few dead drones outside the hive. I hope it means the queen mated and the workers expelled the remaining drones. Still a lot of rain, so inspection will have to wait a couple of days. I will let you know what the outcome is! Thanks.

      • Hello, just a quick message to let you know that I opened the hive – finally! – today. My learning curve will have to pick up with everything I saw. I guess a hive in spring is much different from one in autumn/winter.

        There is a lot of capped brood, workers and drone, so my worries about having no queen have been put to rest. But now there are too many of them! I saw many queen cells in different stages of development, I was at a loss as to what to do! I decided – a bit out of panic – that if they are that set on swarming so be it. Keeping bees is not for the faint hearted! What a challenge. I didn’t want to over inspect and now I feel I under inspected.

        I wasn’t counting on so many things going on already as February was wet, windy and cold. I set out 2 empty hives for the odd chance that if they swarm they will settle close to home. And then I found some varroa mites in some ectopic drone brood I took out and froze to show to my neighbors son and to try to feed to a bunch of wild fire salamander tadpoles growing in a water pool. The good news is that the tadpoles went for the drone larvae and pupa with a vengeance, I never saw them so active!

        But now I need to find what is the varroa status of the hive (I treated with a thymol-based treatment in the Fall). So, to cut a long story short, lots of things to learn and do. But the hive is still going. They showed me they can look after themselves. I will try and do my best to help them out. What a hand full and I only have one hive! It’s fun, though. Thanks.

  • You said “…Some of us are reluctant to have our misfortunes pasted all over the internet…”
    I know that reluctance all too well from working in software development. Developers often get so proud of their work that any criticism, even valid and constructive, is not well received. But what developers have to learn is that criticism isn’t directed at them, personally. It’s directed at the code and is a teachable moment for the developer particularly when the critics offer alternatives along with explanations as to what makes the alternative(s) better.

    So as a researcher & developer, I read your analysis and appreciated the thoroughness in detailing out the possible reasons for the colony’s collapse. but are clear that the failure likely wasn’t a reflection on the keeper. It could’ve been a number of things completely outside of the keeper’s control. Reading his detailed analysis and your thoughts, the only thing within his control would’ve been fall queen damage during an inspection. Since honeybees banish their drones sometime in fall, this tends to make fall inspections a bit more risky and ever since I noticed no drones in my hives, I’ve been very nervous about doing any inspections in fear of crushing or rolling the queen at a time when she can’t be easily replaced by the colony. So how do you, personally, weigh when the positives of doing a late fall inspection outweigh the risk(s)? And what is it that a fall inspection will give you that justifies that risk?

    The other cause you mentioned was Varroa infestation. Some might argue that Varroa treatment was within his control. But based on his thoroughness in this post mortem, I’m assuming he is equally as diligent at Varroa monitoring to know if treatment is required. With no tell-tale signs of Varroa (malformed wings and presence of guanine), I can hardly fault him for not applying treatment. I don’t recall if he mentioned sticky board inspection or not. Since I’ve been uncomfortable digging into my hives this fall, I’ve relied on the screened bottom boards and white insert for monitoring Varroa concentration along with the guidelines in this post:

    • Chris,

      I agree that fall inspection is risky, but I go in until I see some brood, then stop. I start by taking out an end frame, and then sliding and lifting the others while holding them over the box. I just want to see some brood or the queen. If she’s not there, I can order a queen (usually through October) or I combine the colony with another and avoid losing all those bees.

      Plus, if a big hive goes queenless, I don’t want to waste a lot of honey keeping them alive when they are doomed to die. I’d rather combine and give all that honey to the combined hive that has a chance of making it. A big queenless colony can burn through a hundred pounds of honey before it collapses . . . what a waste.

  • Thank you for sharing your experiences and insights about the mysterious case of Aaron’s lost colony. I have two colonies and one may have experienced a similar fate as Aaron’s. On a warm (65 degrees) day last December, I peeked in on my colonies and discovered that one had very few bees in it; the frames were full of honey. Some of the dead bees were in a small cluster clinging to frames. I doubt that the surviving bees will make it through winter, given their small number, which is upsetting given the abundance of their stored honey. I’m now wondering what to do in the new future with the multiple full frames of honey left behind, should the colony disappear altogether. Any suggestions would be most appreciated. Thank you.


    • Marci,

      You could give it to the remaining hive, or you could store it for a backup supply. If you store it, be sure to wrap the frames in plastic and freeze them overnight. If you leave them in the weak hive, remember the honey may attract robbers, wasps, mice, skunks, wax moths—just about anything. So either keep a close eye on the little colony or just give the honey to the larger colony so the bees can police the frames.

      • Thank you for the helpful information on what to do with remaining frames of honey left behind our dwindling colony, should they not make it through the winter. I really appreciate it.

  • Just a thought, I still think it could have been yellowjackets that killed the queen and weakened the colony. When my hive was routed by yellowjackets two years ago, there was no sign of ragged comb because the remaining bees cleaned it up. The only way I knew they had been attacked was because of the piles of dead bodies outside the hive in late fall; bees and yellowjackets in a bout a 20:1 ratio. Many of the bee bodies were missing their heads. Enough bees survived to go into winter, but without their queen they failed. The telltale sign of the missing queen in my hive were several queen cups and a couple supersedure cells. Just a thought, but I wouldn’t rule out yelllowjackets.

    • Kris,

      Fair enough. I think I ruled them out because every time one of my hives has been attacked by yellowjackets, the whole colony was wiped out. But if something stopped the jackets in mid attack, like bad weather, I suppose the bees could recover. Never thought about it because I’ve never seen it. You’re right, too, about the heads. I can’t remember if Aaron reported seeing dead bees or not.

  • I’ll try to answer some of the questions that popped up here and on the other thread when I get back home and am able to look again. Thanks to all – and to you Rusty especially – for your insight and the time it took to review my findings.

    One thing I will mention now is that this hive was a package from April 2014. My other hive is as well. The main difference between the two is that the other one swarmed in June and the one that died out did not. The possibility of a failed queen cannot be ruled out. If I find one in the remnants of the cluster I will let everyone know. I kinda wish I had marked them now… 🙂

  • Just to throw my 2 cents in here… The last photo seems to show a few capped brood cells that would have outlined a small winter brood cluster. To me, that is evidence that the queen was viable till near the end and that the colony was losing population quickly so the brood edges got chilled. I’d suspect viruses exaserbated by Varroa and perhaps pesticides as the colony dwindling agent.

  • Thank you, Aaron! Very brave and great of you to post your photos. We all appreciate it. Nothing worse, for any of us; than a dead-out, but you are making the best of it.

    Thank you, Rusty for you helpful analysis. The only time I had my spring check-up look like this, was when I found no body of a queen. I got several opinions, and the local (more experienced) bee-keepers thought my queen had died in the early fall, and the colony had not had time to make another. They died with a small cluster, surrounded by head’s-in workers; and sadly tons of honey. 🙁

    I have been treatment-free up to now (just essential oils), but i have been super happy to find a no-kill method on your web-site. I have been using ‘sticky paper’ but not finding really any significant varroa population. Now; after ready your material, I realize my error! I have purchased some ‘Mite Away’ for my spring treatments. (just in case)